Computer system having memory device with adjustable data clocking using pass gates

ABSTRACT

A circuit for adjusting a time when data is delivered to a data terminal with respect to an external clock signal includes a data passing circuit and a delay adjusting circuit. The delay adjusting circuit accepts a plurality of control signals each arranged to control passgates arranged in columns, with one column being controlled by a respective one of the control signals. A clock signal passes in parallel manner through a variety of delay gates, and each delay gate is coupled in series with one of the passgates. By selecting a path through desired passgates, one delay path is selected and the delay time added to the clock signal. This delayed clock signal is used to control the data passing circuit, which controls when data is output to the output terminals relative to the original clock signal. The control signals are created by selectively coupling or decoupling the control signals from a static voltage, and fuses or antifuses can be used to facilitate this coupling or decoupling.

TECHNICAL FIELD

[0001] This invention relates to clocked integrated circuits thatdeliver data, and more particularly to a method and apparatus foradjusting the timing of data presented to an output terminal relative toa clock signal.

BACKGROUND OF THE INVENTION

[0002] Clock signals are used by a wide variety of digital circuits tocontrol the timing of various events occurring during the operation ofthe digital circuits. For example, clock signals are used to designatewhen command signals, data signals, and other signals used in memorydevices and other computer components are valid and can thus be used tocontrol the operation of the memory device or computer system. Forinstance, a clock signal can be used to develop sequential columnaddresses when an SDRAM is operating in burst mode.

[0003] Retrieving valid data from a clocked memory device at a specifiedtime can be difficult to coordinate. After a memory address is selected,the data travels out of the selected memory cell, is amplified, passesthrough configuration circuitry (if the memory chip has multipleconfigurations) and passes through an output buffer before the data isread. Before the advent of synchronous memory circuits, data simplyappeared at an output terminal following a propagation delay after thedata was requested. In a synchronous memory circuit, data delivery issynchronized with a clock signal. Many circuits have been created tocoordinate data signals with clock signals, with varying degrees ofsuccess. Two of the problems to solve are determining how fast and withwhat regularity the data signal propagates through the chip circuitry.Because data output is often coordinated with a clock signal that isexternal to the memory chip, computer simulations of signal propagationwithin a chip are performed to align the external clock signal with thedata delay of the synchronous memory device. Static time delays are thendesigned into the memory circuit based on the simulation predictions.Because of production variations, improper assumptions, and otherfactors ultimately causing timing errors, the data does not alwaysarrive at the output terminal at the desired time. As computer clockspeeds increase, the window for providing valid data to the outputterminal closes, making it more difficult to ensure the correct deliverytime of data from the memory circuit.

[0004] An example of a circuit that provides data to a data pad at aspecific time relative to an external clock is shown in FIG. 1. Anoutput circuit 2 includes a memory array 5 that contains an array ofindividual memory cells (not shown). Once a particular memory cell isselected to be read, complementary signals corresponding to the contentsof the memory cell travel to a pair of respective I/O and I/O* lines.The signals on the I/O and I/O* lines are sensed and amplified by a datasensing circuit 10, which produces a DATA* signal at an output, Anexternal clock signal is received at a clock circuit input 7 and passesthrough clock circuitry 15 to become a CLKDOR* signal. The CLKDOR*signal may differ from the external clock signal in a variety of ways,including phase, orientation, and duty cycle, however, their overallperiodic cycle length is the same. Oftentimes, to properly match timingof the data arriving at the data pad with the external clock signal, astatic delay is added within the clock circuitry 15.

[0005] The DATA* signal is presented to a passgate 20 and passed to anoutput node 21 when the signal CLKDOR* signal is HIGH and its complementfrom an inverter 17 is LOW. From the output node 21, the DATA* signal isinput to a NOR gate 30 along with a TRISTATE signal. An output from theNOR gate 30 leads to a passgate 24. When the CLKDOR* signal is LOW andits complement from the inverter 17 is HIGH, the output from the NORgate 30 passes through the passgate 24 and becomes the signal DQHI.Another NOR gate 32 combines the output of the NOR gate 30 with theTRISTATE signal. This output from the NOR gate 32 is presented to a pairof passgates 22, 26. The passgate 22 receives the signal from the NORgate 32 and, when the CLKDOR* signal is LOW and its complement from theinverter 17 is HIGH, feeds it back to the output node 21. The passgate26 passes the signal it receives from the NOR gate 32 as an outputsignal DQLO when the signal CLKDOR* is LOW and its complement from theinverter 17 is HIGH.

[0006] If the signal DQHI is HIGH, a pull-up circuit 36 raises a DQ pad40 to a HIGH voltage. Conversely, if DQLO is HIGH, it activates apull-down circuit 38 to pull the DQ pad 40 to a ground voltage. Theoutput circuit 2 is designed so that the pull-up circuit 36 and thepull-down circuit 38 cannot operate simultaneously. When neither thepull-up circuit 36 nor the pull-down circuit 38 is active, the DQ pad 40is neither pulled up to a HIGH voltage nor pulled down to ground, butinstead remains in a high-impedance state.

[0007] The circuit operation of the data delivery circuit 2 will now beexplained. When the CLKDOR* signal is HIGH and the DATA* signal is HIGH,a HIGH signal passes to the output node 21. Assuming that the TRISTATEsignal is low to enable the NOR gates 30 and 32 so they act asinverters, when the CLKDOR* signal goes LOW, the passgate 22 couples theoutput of the NOR gate 32 to the input of the NOR gate 30, output node21. The NOR gates 30 and 32 then latch the HIGH at the output node 21 tothe output of the NOR gate 32. At the same time, a LOW is latched to theoutput of the NOR gate 30. The HIGH at the output of the NOR gate 32 iscoupled through the passgate 26 to the pull-down circuit 38. The HIGHsignal DQLO causes the pull-down circuit 38 to pull the DQ pad 40 toground. At the same time, the LOW signal at the output of the NOR gate30 passes through the passgate 24. The LOW DQHI signal does not activatethe pull-up circuit 36, as explained above. Alternatively, if the DATA*signal is LOW, a LOW signal is passed to the output node 21 when theCLKDOR* signal is HIGH. When the CLKDOR* signal drops LOW, the LOWsignal at the output node 21 is latched by the NOR gates 30 and 32, isfed back to the output node 21 through the passgate 22, and alsopropagates through the passgate 26 to make DQLO LOW. Concurrently, theLOW signal at the data output node 21 causes the NOR gate 30 to output aHIGH signal that passes through the passgate 24 to provide a HIGH DQHIsignal. The HIGH DQHI signal causes the pull-up circuit 36 to connectthe DQ pad 40 to a HIGH voltage. If the TRISTATE signal is HIGH, neitherDQHI nor DQLO will be HIGH regardless of the state of the DATA* signal.Thus, the DQ pad 40 floats in a high impedance state.

[0008] When a computer system is designed, specifications for signaltiming are determined. Some of the signals and timings used in thedesign are shown in FIG. 2. One of the design specifications is anaccess time, T_(AC), used to designate a maximum time between a risingedge of an external clock signal and when a valid data signal arrives atthe DQ pad 40. Additionally, another specified time parameter is theoutput hold time, T_(OH), indicative of a minimum time for how long thedata will be held at the DQ pad 40 following a subsequent rising edge ofthe external clock. For example, as illustrated in FIG. 2, a READcommand signal is input to a memory circuit sometime between a risingedge of a clock pulse CP0 and a clock pulse CP1. At a time CP1, the READcommand is latched and read by the memory circuit, indicating data is tobe read from a memory cell in a memory array. The data is read from thearray and placed at the DQ pad 40 under the control of the CLKDOR*signal. The specification T_(AC) indicates a maximum time until thedesired data is placed on the DQ pad 40. The data is held at the DQ pad40 for a time no less than the specification T_(OH), as measured from asubsequent clock pulse after the READ command is latched. As shown inFIG. 2, T_(AC1) is the time measured from CP2 until Data₁ is stable onthe DQ line. T_(AC2) is the time measured from CP3 until Data₂ is stableon the DQ line, and so on. The time T_(AC1) will be nearly identical tothe other access times T_(AC2), T_(AC3), etc. under the same operatingconditions. Also shown in FIG. 2, T_(OH1)I is the time measured from thenext clock pulse following when Data₁ appears on the DQ line, i.e., CP3,to the time when Data-hd 1 , begins to transition off the DQ line. Asabove, the measured hold times T_(OH2), T_(OH3), etc. will be nearlyidentical to one another under similar operating conditions.

[0009] During the design phase of a memory chip, a designer determineshow much after each clock pulse the CLKDOR* signal should fire. Thisdelay determines when the data is made available on the DQ line relativeto the external clock signal. Typically, a delay value is chosen thatprovides a tolerance for both the T_(AC) and T_(OH) parameters. If theCLKDOR* signal fires too soon after the external clock signal, the chipwill easily pass the T_(AC) specification, but may fail the T_(OH)specification. If the CLKDOR* signal fires too late, the chip willeasily pass the T_(OH) specification but may fail the T_(AC)specification. These time compensations, by virtue of being fabricatedas part of the circuit, generally cannot be changed after manufacture ofan integrated circuit. When memory chips fail their timingspecifications, they are sold as lesser quality chips for a reducedprice, or even destroyed. Thus, there is an economic incentive tomaximize the number of chips that meet or exceed the timingspecifications. As a consequence of increasing computer speeds, thisalready small window for proper data timing is reducing. Because ofprocess variations, errors in design assumptions, the wide range oftemperatures and voltages in which the chips are warrantied to perform,and other factors, an increasing number of memory chips fail to meet theincreasingly stringent design specifications.

SUMMARY OF THE INVENTION

[0010] An adjustable data delay circuit comprises a clocked data passingcircuit that receives a clock signal and a data signal. An adjustabletime delay circuit is coupled to the clock signal for adjusting the timethe data is delivered to an output terminal relative to the clocksignal. The adjustable time delay circuit includes a plurality of delaygates, each individually selected by control signals. One path in thetime delay circuit that includes the desired delay gate is selected bythe control signals. The clock signal passing through the selected delaygate is then used to control the time when the data is delivered to theoutput terminal.

[0011] In one embodiment, the control signals are made by selectivelycoupling a pattern of control inputs to a reference voltage.

[0012] In another embodiment, the passgates are arranged in a pluralityof columns such that each column has a number of passgates that is aninteger power of 2.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic diagram of a conventional clocked datadelivery circuit.

[0014]FIG. 2 is a timing diagram of various signals during the operationof the clocked data circuit of FIG. 1.

[0015]FIG. 3 is a schematic diagram of an adjustable clocked datacircuit according to one embodiment of the present invention.

[0016]FIG. 4A is a schematic diagram of a delay adjusting circuitaccording to one embodiment of the present invention.

[0017]FIG. 4B is a chart showing how different delay times are selectedusing one embodiment of the present invention.

[0018]FIG. 5A is a schematic diagram of a conventional adjustableimpedance device.

[0019]FIG. 5B is a schematic diagram of another conventional adjustableimpedance device.

[0020]FIG. 6 is a block diagram of a synchronous dynamic random accessmemory including the adjustable time delivery circuit of FIG. 3.

[0021]FIG. 7 is a block diagram of a computer system including therandom access memory of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0022] One embodiment of an adjustable time delay circuit 102 inaccordance with the invention is illustrated in the schematic diagram ofFIG. 3. The adjustable delay circuit 102 includes some of the samecomponents as the output circuit 2, shown in FIG. 1. Identicalcomponents of the output circuit 2 and the adjustable time circuits 102have been given the same reference numbers, and for the sake of brevity,identical components will not be described in further detail. Theadjustable time data circuit 102 includes a delay adjusting circuit 60located between the clock circuitry 15 and the control inputs to thepassgates 20, 22, 24, and 26. As later described, the delay adjustmentcircuit 60 can be located in various places in the adjustable delaycircuit 102, and is shown in this location of the adjustable delaycircuit 102 for illustration.

[0023] As shown in FIG. 4A, the CLKDOR* signal is input to the delayadjusting circuit 60 at an input terminal 62. From there it is splitinto four paths, passing through a delay circuit 70, having a delay of1.0; a delay circuit 72, having a delay of 0; a delay circuit 74, havinga delay of 0.5; and a delay circuit 76, having a delay of 1.5. The delaytimes 0, 0.5, 1.0, and 1.5 are an indication of relative measure and donot necessarily indicate a specific time period. These delay times areselected such that the delay that would have been designed into theoutput circuit 2 appears as a middle value of the range of delay valueseligible for selection. In this way, the data delivery of a memory chipcan be “accelerated” by selecting a delay time shorter than the built-indelay of the prior art circuit, or “decelerated” by selecting a delaytime longer than the built-in delay of the prior art circuit. The outputsignals from the delay circuits 70, 72, 74, and 76 are input to apassgate 80, a passgate 82, a passgate 84, and a passgate 86,respectively. The passgates 80, 82, 84, and 86 are controlled by acontrol signal A and its complement formed by passing A through aninverter 92. The signals from the passgates 80 and 82 combine as aninput to a passgate 88, and the signals from the passgates 84 and 86combine as an input to a passage 90. The outputs from the passgates 88and 90 connect at an output terminal 95, and form an output signal OUT.The passgates 88, and 90 are controlled by a control signal B and itscomplement formed by passing B through an inverter 94.

[0024] Referring back to FIG. 2, the benefits of having an adjustableCLKDOR* signal will be described. As previously stated, adding delay tothe CLKDOR* signal in relation to the CLK signal allows the designer toprovide a tolerance for the T_(AC) and T_(OH) specifications. After thechip is produced, the T_(AC) and T_(OH) specifications, and others, aretested. If the chip does not pass all of the specifications, it cannotbe sold at the current market price for the highest quality chips. Byincluding an adjustable timing circuit within the memory chip, chipsthat do not meet the T_(AC) and T_(OH) specifications after manufacturemay be able to be adjusted in order to meet the specifications.

[0025] For example, the specifications may direct that T_(AC) can be nomore than 6 ns and T_(OH) cannot be less than 3 ns. Assume that T_(AC1)measured 4 ns and T_(OH1) measured 2.5 ns. The specification for T_(AC)is easily passed (the shorter the better), but the chip fails the T_(OH)specification because it does not hold the data for a long enough timeon the DQ lines. By adding a Ins delay to the time when the CLKDOR*signal fires, the chip can be brought within the specifications. TheT_(AC1) increases to 5 ns (still passing the 6 ns specification) and theT_(OH1) increases to hold the data valid on the DQ lines for 3.5 ns,passing the 3 ns specification.

[0026] The delay adjusting circuit 60 of FIG. 4A is controlled bycontrol signals A and B. These control signals provide a HIGH or LOWsignal to the passgates depending on a state of a respective adjustableimpedance circuit 96. Two different kinds of adjustable impedancedevices are shown, one in FIG. 5A and one in FIG. 5B. One type ofadjustable impedance circuit 96 is a circuit containing an antifuse 65,shown in FIG. 5A. The antifuse 65 is made from a pair of conductingplates 110 and 112 separated by a dielectric material 115. Antifuses aredevices similar to small capacitors. They have a natural and a blownstate. When the antifuse 65 is in a natural state, the dielectricmaterial 115 electrically insulates the pair of plates 110 and 112.Because the dielectric material 115 is intact, the node C iselectrically insulated from the ground voltage. To change the antifuse65 to its blown state, a high electric field is passed across thedielectric material 115 by raising C_(gnd) to a programming voltage, forexample, 10 volts, while enabling a PROGRAM transistor. This is usuallydone after chip fabrication and packaging, but can be completed beforepackaging. When the high electric field is placed across the dielectricmaterial 115, it breaks down and loses its insulative properties. Thisallows the plates 110 and 112 to contact one another creating arelatively low resistive contact. When blown, the antifuse 65 couplesthe node C to the node C_(gnd), that is normally held at the groundvoltage, unless the antifuse is being programmed, as described above. Totest the state of the antifuse 65 a Read* signal is strobed LOW. Thatconnects node C to the Vcc voltage. If the antifuse 65 is blown, thenode C is quickly brought down to ground. An inverter 50 causes a HIGHsignal to be sent to a BLOWN output. The HIGH signal also keeps a HOLDtransistor OFF. Conversely, if the antifuse 65 is in its natural state,node C will not be pulled down to ground and BLOWN will carry a LOWsignal. This low signal also enables the HOLD transistor, keeping node Cat the voltage Vcc.

[0027] The other adjustable impedance circuit 96, shown in FIG. 5Bcontains a fuse 68. The fuse 68 also has a natural and a blown state. Inits natural state, the fuse 68 couples a node D to the ground voltage.The fuse 68 is blown by passing a high current through it, or by someother means such as cutting it with a laser, for example. When the fuse68 is blown, the node D is disconnected from the ground voltage. As withthe antifuse 65, the fuse 68 may be blown before or after packaging.Also as described above, the adjustable impedance circuit 96 of FIG. 5Bis read in a similar manner. The Read* signal strobes LOW raising a nodeD to the Vcc voltage. If the fuse 68 is intact, node D is coupled toground and BLOWN is LOW. This LOW signal passes through an inverter 52to keep the HOLD transistor OFF. If the fuse is blown, node D is chargedto Vcc and BLOWN is pulled HIGH.

[0028] Referring back to FIG. 4A, the adjustable impedance circuits 96may be either of the structures shown in FIG. 5A or 5B. By coupling thesignals A and B to a voltage using antifuses 65 or fuses 68, themanufacturer can easily select the signals A and B to be either HIGH orLOW, as desired. Although described here as controlling only oneadjustable delay circuit 102, a single delay adjusting circuit 60 may beused to adjust any or all of the adjustable delay circuits within amemory chip, thereby controlling the data delivery time at any or all ofthe DQ pads on the memory chip.

[0029] The operation of the delay adjusting circuit 60 will now bedescribed. In operation, one of the four delay times is selected throughthe states of signals A and B, as shown in the chart in FIG. 4B. If Aand B are each connected to respective adjustable impedance circuits 96that are BLOWN, both A and B will be HIGH, indicated as “1” in FIG. 4B.This places the passgates 82, 86, and 90 in a passing state. Because thepassgates 86 and 90 are passing, the signal CLKDOR* passes through thedelay gate 76 having a delay of 1.5, and through the passgates 86 and 90to the output terminal 95. The CLKDOR* signal also passes through thedelay gate 72, having no delay and through the passgate 82, but isblocked at the passgate 88, which is in a blocking state by virtue of aHIGH B signal and a LOW signal received from the inverter 94. Byselecting the states of the signals A and B (by selectively adjustingthe impedance circuits 96), it is easy to adjust the time delay of aclock signal input to the delay adjusting circuit 60. In one embodiment,the delay time selected by keeping the adjustable impedance circuits 96in their natural state will be the delay most likely to provide thegreatest tolerances for both T_(AC) and T_(OH). In FIG. 4A this desireddelay is 1.0. In this way, the majority of the memory chips will passthe T_(AC) and T_(OH) specifications without further adjustment, savinglabor and equipment costs. Only in the extraordinary case will the delayneed adjustment. Although shown here with only two columns of passgatescontrolled by the signals A and B, it is apparent that a greaterselection of delay times can be made available with the addition of morecontrol signals and more passgates, or that the passgates could have adifferent configuration. For instance, eight different delay times areefficiently selectable if three control signals are used, with threecolumns, one each containing two, four and eight passgates.

[0030] Although the delay adjusting circuit 60 is shown after the clockcircuitry 15, it can appear in many locations in a synchronized memorycircuit, some of which are illustrated in FIG. 3. For instance, thedelay adjusting circuit 60 can appear directly before the clockcircuitry 15. If the delay adjusting circuit 60 is placed after thepassgates 24 and 26, the delay adjusting circuit must be implemented inpairs because the data has two separate paths. Only one delay adjustingcircuit 60 is needed if it is located between an output terminal 37 andthe DQ pad 40. Of course, there are other locations where the delayadjusting circuit 60 could be placed, as long as it is between the clocksignal input 7 and the DQ pad 40.

[0031] A synchronous dynamic random access memory (SDRAM) 200 using theadjustable time delay circuit 102 of FIG. 3 is shown in FIG. 6. TheSDRAM 200 has a control logic circuit 202 receiving a clock signal CLKand a clock enable signal CKE. In the SDRAM 200, all operations arereferenced to a particular edge of an internal clock signal ICLK and adata read clock CLKDOR*, both generated from the clock signal CLK. Theedge of the ICLK signal that is used is typically the rising edge, whilethe data read operations are referenced to the falling edge of theCLKDOR*, as known in the art. The delay adjusting circuit 60 ispreferably included in the control logic 202 to adjust the timing of thedata read clock CLKDOR* relative to the clock signal CLK. In practice, avariety of internal clock signals may be generated from the clock signalCLK, and only some of them may have their timing controlled by the delayadjusting circuit 60. However, in the interest of brevity, only twointernal clock signals, ICLK and CLKDOR* are shown. The control circuit202 further includes a command decode circuit 204 receiving a number ofcommand signals on respective external terminals of the SDRAM 200. Thesecommand signals typically include a chip select signal {overscore (CS)},write enable signal {overscore (WE)}, column address strobe signal{overscore (CAS)}, and row address strobe signal {overscore (RAS)}.Specific combinations of these signals define particular data transfercommands of the SDRAM 200 such as ACTIVE, PRECHARGE, READ, and WRITE asknown in the art. An external circuit, such as a processor or memorycontroller generates these data transfer commands to read data from andto write data to the SDRAM 200.

[0032] The SDRAM 200 further includes an address register 206 operableto latch an address applied on an address bus 208, and output thelatched address to the control circuit 202, a column address latch 210,and a row address multiplexer 212. During operation of the SDRAM 200, arow address with a bank address BA and a column address with the bankaddress are sequentially latched by the address register 206 undercontrol of the control circuit 202. In response to the latched bankaddress BA and row address, the control circuit 202 controls the rowaddress multiplexer 212 to latch and output the row address to one of arow address latch 214 and 216. The row address latches 214 and 216, whenactivated, latch the row address from the row address multiplexer 212and output this latched row address to an associated row decoder circuit222 and 224, respectively. The row decoder circuits 222 and 224 decodethe latched row address and activate a corresponding row of memory cellsin memory banks 218 and 220, respectively. The memory banks 218 and 220each include a number of memory cells (not shown) arranged in rows andcolums, each memory cell operable to store a bit of data and having anassociated row and column address.

[0033] When a column address and bank address BA is applied on theaddress bus 208, the column address is latched by the address register206 under control of the control circuit 202, and output to a columnaddress latch 210, which latches the column address and in turn outputsthe column address to a burst counter circuit 226. The burst countercircuit 226 operates to develop sequential column addresses beginningwith the latched column address when the SDRAM 200 is operating in aburst mode. The burst counter 226 outputs the developed column addressesto a column address buffer 228, which in turn outputs the developedcolumn address to a pair column decoder circuits 230 and 231. The columndecoder circuits 230 and 231 decode the column address and activates oneof a plurality of column select signals 232 corresponding to the decodedcolumn address. The column select signals 232 are output to senseamplifier and I/O gating circuits 234 and 236 associated with the memorybanks 218 and 220, respectively. The sense amplifier and I/O gatingcircuits 234 and 236 sense and store the data placed on the digit lines235 and 237, respectively, by the memory cells in the addressed row andto thereafter couple the digit lines 235 or 237 corresponding to theaddressed memory cell to an internal data bus 238. The internal data bus238 is coupled to a data bus 240 of the SDRAM 200 through either a datainput register 242 or a data output register 244. In the preferredembodiment, the adjustable time delay circuit 102 is coupled to the dataoutput register 244. This circuit is used to adjust the time data ispresented to the data bus in reference to the clock signal CLK. A datamask signal DQM controls the circuits 234 and 236 to avoid datacontention on the data bus 240 when, for example, a READ command isfollowed immediately by a WRITE command, as known in the art.

[0034] In operation, during a read data transfer operation, an externalcircuit, such as a processor, applies a bank address BA and row addresson the address bus 208 and provides an ACTIVE command to the commanddecode circuit 204. This applied address and command information islatched by the SDRAM 200 on the next rising edge of the clock signalCLK, and the control circuit 202 thereafter activates the addressedmemory bank 218 or 220. The supplied row address is coupled through therow address multiplexer 212 to the row address latch 214 or 216associated with the addressed bank, and this row address is thereafterdecoded and the row of memory cells in the activated memory bank 218 or220 is activated. The sense amplifiers in the sense amplifier and I/Ogating circuit 234 or 236 sense and store the data contained in eachmemory cell in the activated row of the addressed memory bank 218 or220.

[0035] The external circuit thereafter applies a READ command to thecommand decode circuit 204 including a column address and bank addressBA on the address bus 208, both of which are latched on the next risingedge of the clock signal CLK. The latched column address is then routedthrough the circuits 210, 226, and 228 to the column decoder circuit 230under control of the control circuit 204. The column decoder 230 decodesthe latched column address and activates the column select signal 232corresponding to that decoded column address. In response to theactivated column select signal 232, the sense amplifier and I/O gatingcircuit 234 or 236 transfers the addressed data onto the internal databus 238, and the data is then transferred from the internal data bus 238through the data output register 244 and onto the data bus 240 where itis read by the external circuit.

[0036] During a write data transfer operation, after activating theaddressed memory bank 218 or 220 and the addressed row within that bank,the external circuit applies a WRITE command to the command decodecircuit 204 including a column address and bank address BA on theaddress bus 208 and data on the data bus 240. The WRITE command, columnaddress, and data are latched respectively into the command decodecircuit 204, address register 206, and data input register 242 on thenext rising edge of the clock signal CLK or an internal clock signal notgenerated by the delay adjusting circuit 60. The data latched in thedata input register 242 is placed on the internal data bus 238, and thelatched column address is routed through the circuits 210, 226, and 228to the column decoder circuit 230 under control of the control circuit204. The column decoder 230 decodes the latched column address andactivates the column select signal 232 corresponding to that decodedaddress. In response to the activated column select signal 232, the dataon the internal data bus 238 is transferred through the sense amplifierand I/O gating circuit 234 or 236 to the digit lines 235 or 237corresponding to the addressed memory cell. The row containing theaddressed memory cell is thereafter deactivated to store the writtendata in the addressed memory cell.

[0037] Although the adjustable time delay circuit 102 has been describedas being used in the SDRAM 200, it will be understood that it may alsobe used in other types of integrated circuits such as synchronousgraphics RAM (SGRAM), or synchronous static RAM (synchronous SRAM).Those skilled in the art realize the differences between SDRAM and othertypes of memories, and can easily implement the adjustable time delaycircuit 102.

[0038]FIG. 7 is a block diagram of a computer system 300 including theSDRAM 200 of FIG. 5. The computer system 300 includes a processor 302for performing various computing functions, such as executing specificsoftware to perform specific calculations or tasks. Coupled to theprocessor 302 is a synchronous SRAM circuit 303, used for a memory cacheor other memory functions. In addition, the computer system 300 includesone or more input devices 304, such as a keyboard or a mouse, coupled tothe processor 302 to allow an operator to interface with the computersystem 300. Typically, the computer system 300 also includes one or moreoutput devices 306 coupled to the processor 302, such output devicestypically being a printer or a video terminal. One or more data storagedevices 308 are also typically coupled to the processor 302 to storedata or retrieve data from external storage media (not shown). Examplesof typical data storage devices 308 include hard and floppy disks, tapecassettes, compact disk read-only memories (CD-ROMs), and digitalvideodisk read-only memories (DVD-ROMs). The processor 302 is typicallycoupled to the SDRAM 200 and to the synchronous SRAM 303 through acontrol bus, a data bus, and an address bus to provide for writing datato and reading data from the SDRAM and synchronous SRAM. A clockingcircuit (not shown) typically develops a clock signal driving theprocessor 302, SDRAM 200, and synchronous SRAM 303 during such datatransfers.

[0039] It is to be understood that even though various embodiments andadvantages of the present invention have been set forth in the foregoingdescription, the above disclosure is illustrative only, and changes maybe made in detail, and yet remain within the broad principles of theinvention. Therefore, the present invention is to be limited only by theappended claims.

1. A data delay circuit comprising: an external clock terminal adaptedto receive an external clock signal having a first state and a secondstate; a data terminal adapted to receive a data signal; an adjustabletime delay circuit having one or more control inputs each adapted toreceive a control signal, the time delay circuit adapted to receive theexternal clock signal at a clock input and pass a delayed clock signalto an output terminal, the time between when the external clock signalchanges states and when the delayed clock signal changes statesdetermined by the control signals received at the control inputs; and adata passing circuit receiving both the data signal and the delayedclock signal, the data passing circuit adapted to pass the data signalfrom the data terminal to a data output terminal after the delayed clocksignal changes from the first to the second state.
 2. The circuit ofclaim 1 wherein the control signals are generated by selectivelycoupling the control inputs to a reference voltage.
 3. The circuit ofclaim 2 wherein each of the control inputs is selectively coupled to areference voltage using a respective fuse.
 4. The circuit of claim 2wherein each of the control inputs is selectively coupled to a referencevoltage using a respective antifuse.
 5. The circuit of claim 1 whereinthe adjustable time delay circuit further comprises: a plurality ofpassgates arranged in columns, each column having a different number ofpassgates than any other column in the time delay circuit, the passgatesin the column having the highest number of passgates in the delaycircuit each coupled to a respective delay element having a respectivedelay value, and the external clock signal coupled to and passingthrough each of the delay elements.
 6. The circuit of claim 5 whereinone of the delay elements has a null delay value.
 7. The circuit ofclaim 5 wherein each of the columns is coupled to the columns adjacentto it such that one-half of the total number of passgates in each columnare coupled to one-half of the total number of passgates in eachadjacent column.
 8. The circuit of claim 5 wherein the number of controlinputs to the delay circuit is n, the number of columns in the timedelay circuit is n, and the number of passgates in the column having thehighest number of passgates in the delay circuit 2^(n).
 9. The circuitof claim 5 wherein each control signals controls all of the passgates ina respective one of the columns, with one-half of the passgates in therespective column controlled to a passing state and the remainder of thepassgates in the respective column controlled to a blocking stateresponsive to the respective control signal.
 10. A clocked-data phaseadjustment circuit comprising: a reference clock terminal adapted toreceive a reference clock signal having a first state and a secondstate; a data terminal adapted to receive a data signal; a phaseshifting circuit adapted to receive one or more control signals, thereference clock signal, and the data signal each at respective inputs,and the phase shifting circuit adapted to adjust the time when a delayeddata signal is passed from the data input terminal to a data outputterminal relative to the phase of the reference clock signal, the phasedelay between when the reference clock signal changes states and whenthe delayed data signal is passed determined by the control signals. 11.The circuit of claim 10 wherein the control signals are generated byselectively coupling the control inputs to a reference voltage.
 12. Thecircuit of claim 11 wherein each of the control inputs is selectivelycoupled to a reference voltage using a respective fuse.
 13. The circuitof claim 11 wherein each of the control inputs is selectively coupled toa reference voltage using a respective antifuse.
 14. The circuit ofclaim 10 wherein the phase shifting delay circuit further comprises: aplurality of passgates arranged in columns, each column having adifferent number of passgates than any other column in the phaseshifting circuit, the passgates in the column having the highest numberof passgates in the delay circuit each coupled to a respective delayelement having a respective delay value, and the external clock signalcoupled to and passing through each of the delay elements.
 15. Thecircuit of claim 14 wherein one of the delay elements has a null delayvalue.
 16. The circuit of claim 14 wherein each of the columns iscoupled to the columns adjacent to it such that one-half of the totalnumber of passgates in each column are coupled to one-half of the totalnumber of passgates in each adjacent column.
 17. The circuit of claim 14wherein the number of control inputs to the delay circuit is n, thenumber of columns in the time delay circuit is n, and the number ofpassgates in the column having the highest number of passgates in thedelay circuit is 2^(n).
 18. The circuit of claim 14 wherein each controlsignals controls all of the passgates in a respective one of thecolumns, with one-half of the passgates in the respective column in apassing state and the remainder of the passgates in the respectivecolumn in a blocking state responsive to the respective control signal.19. In a synchronous memory circuit, a circuit to adjust output datatiming comprising: an external clock terminal adapted to receive anexternal clock signal having a first state and a second state; a clockfiltering circuit coupled to the external clock terminal, the clockfiltering circuit adapted to modifying the external clock signal into adata clock signal; a data terminal adapted to receive a data signal; anadjustable time delay circuit having one or more control inputs eachhaving a control signal, the time delay circuit adapted to receive thedata clock signal at a clock input and pass a time adjusted data clocksignal to an output terminal, the time between when the data clocksignal changes states and when the time adjusted data clock signalchanges states determined by the control signals received at the controlinputs; and a data passing circuit adapted to receive both the datasignal and the time adjusted data clock signal, the data passing circuitadapted to pass the data signal from the data terminal to a data outputterminal after the time adjusted data clock signal changes from thefirst to the second state.
 20. The circuit of claim 19 wherein thecontrol signals are generated by selectively coupling the control inputsto a reference voltage.
 21. The circuit of claim 19 wherein theadjustable time delay circuit further comprises: a plurality ofpassgates arranged in columns, each column having a different number ofpassgates than any other column in the time delay circuit, the passgatesin the column having the highest number of passgates in the delaycircuit each coupled to a respective delay element having a respectivedelay value, the external clock signal coupled to and passing througheach of the delay elements.
 22. The circuit of claim 21 wherein thenumber of control inputs to the delay circuit is n, the number ofcolumns in the time delay circuit is n, and the number of passgates inthe column having the highest number of passgates in the delay circuitis 2^(n).
 23. The circuit of claim 19 wherein the synchronous memorycircuit is a synchronous static random access memory.
 24. A synchronousmemory device comprising: an address bus; a control bus; a data bus; aclock terminal adapted to receive a clock signal; a clock enableterminal adapted to receive a clock enable signal; an address decodercoupled to the address bus; a control logic circuit coupled to thecontrol bus; a read/write circuit coupled to the data bus; a memory-cellarray coupled to the address decoder, control circuit, and read/writecircuit, including a plurality of row lines; a plurality of pairs offirst and second complementary digit lines; an array of memory cellsthat each have a control terminal coupled to one of the row lines and adata terminal coupled to one of the first and second complementary digitlines of one of the pairs of complementary column lines; and a datadelay circuit comprising an external clock terminal adapted to receivean external clock signal having a first state and a second state, a dataterminal adapted to receive a data signal, an adjustable time delaycircuit having one or more control inputs each adapted to receive acontrol signal, the time delay circuit adapted to receive the externalclock signal at a clock input and pass a delayed clock signal to anoutput terminal, the time between when the external clock signal changesstates and when the delayed clock signal changes states determined bythe control signals received at the control inputs, and a data passingcircuit receiving both the data signal and the delayed clock signal, thedata passing circuit adapted to pass the data signal from the dataterminal to a data output terminal after the delayed clock signalchanges from the first to the second state.
 25. The circuit of claim 24wherein the control signals are generated by selectively coupling thecontrol inputs to a reference voltage.
 26. The circuit of claim 24wherein the adjustable time delay circuit further comprises: a pluralityof passgates arranged in columns, each column having a different numberof passgates than any other column in the time delay circuit, thepassgates in the column having the highest number of passgates in thedelay circuit each coupled to a respective delay element having arespective delay value, the external clock signal coupled to and passingthrough each of the delay elements.
 27. The circuit of claim 26 whereinthe number of control inputs to the delay circuit is n, the number ofcolumns in the time delay circuit is n, and the number of passgates inthe column having the highest number of passgates in the delay circuitis 2^(n).
 28. The circuit of claim 24 wherein the synchronous memorydevice is a synchronous dynamic random access memory.
 29. A computersystem comprising: a data input device; a data output device; an addressbus; a data bus; a control bus; and computing circuitry coupled to thedata input and output devices, and the data, address and control busses,the computing circuitry including: a data delay circuit comprising anexternal clock terminal adapted to receive an external clock signalhaving a first state and a second state, a data terminal adapted toreceive a data signal, an adjustable time delay circuit having one ormore control inputs each adapted to receive a control signal, the timedelay circuit adapted to receive the external clock signal at a clockinput and pass a delayed clock signal to an output terminal, the timebetween when the external clock signal changes states and when thedelayed clock signal changes states determined by the control signalsreceived at the control inputs, and a data passing circuit receivingboth the data signal and the delayed clock signal, the data passingcircuit adapted to pass the data signal from the data terminal to a dataoutput terminal after the delayed clock signal changes from the first tothe second state.
 30. The circuit of claim 29 wherein the controlsignals are generated by selectively coupling the control inputs to areference voltage.
 31. The circuit of claim 29 wherein the adjustabletime delay circuit further comprises: a plurality of passgates arrangedin columns, each column having a different number of passgates than anyother column in the time delay circuit, the passgates in the columnhaving the highest number of passgates in the delay circuit each coupledto a respective delay element having a respective delay value, theexternal clock signal coupled to and passing through each of the delayelements.
 32. The circuit of claim 31 wherein the number of controlinputs to the delay circuit is n, the number of columns in the timedelay circuit is n, and the number of passgates in the column having thehighest number of passgates in the delay circuit is 2^(n).
 33. A methodof adjusting the time data is delivered to an output terminal of amemory circuit after the memory circuit has been fabricated, the methodcomprising the steps of: accepting a data signal at a data input;accepting a clock signal at a clock input; selecting a delay time to beadded to the clock signal to generate a delayed clock signal; and usingthe delayed clock signal to control the time when the data signal ispassed to a data output.
 34. The method of claim 34 wherein the delaytime selected is one of a plurality of pre-selected delay times.
 35. Themethod of claim 34 wherein the step of selecting a delay time furtherincludes the step of selectively coupling control inputs to a controlvoltage, the control inputs coupled to and controlling a plurality ofpassgates such that for any single pattern of coupled control inputs,there exists only one path through a controllable delay circuit.